Enter address and prefix
Use dotted IPv4 with a /0 through /32 prefix, or switch to mask or host sizing.
One address · exact boundaries
Turn IPv4 and CIDR into a subnet you can verify.
Enter an IPv4 address and prefix to see the network, mask, wildcard, first and last usable address, broadcast behavior, and counts. SubnetCalc works locally with explicit ordinary, /31 point-to-point, and /32 host-route rules—without account, lookup, saved URL, or live network access.
No IP lookup, scanning, account, history, backend calculation, or indexed result URL.
Three visible steps
Enter, calculate, verify
Make the address context explicit
Ordinary subnets reserve network and broadcast. /31 uses two endpoints only when point-to-point is selected; /32 is a host route.
Check every boundary
Read the mask, wildcard, network, range, broadcast behavior, and counts from one auditable result.
Six focused searches
Use the page that matches your question
- Calculate network, broadcast, and usable range from IPv4/CIDR.
- Convert a prefix to a contiguous mask—or a valid mask back to CIDR.
- Find the smallest ordinary subnet for a required usable-host count.
- Review every prefix in one chart and the three RFC 1918 private blocks.
Use your own subnet
Keep every boundary visible
Enter one IPv4 address and prefix. SubnetCalc calculates locally and keeps the mask, range, counts, and special /31 or /32 rule beside the answer.